Hi I'm Sadlo, aka a boosted mythic raider and 2k io Fire/Frost Mage. I was 5.5k io in legion before the artifact buff as well.

This is just a general idea on what I do personally, from dungeon to dungeon and affix to affix things change and over time you'll learn how to adjust to these and pick what pew pews better.
Feel free to post questions here if you have any and I'll try to respond as I can. I'm not the best mage and I'm sure someone could post a better guide, but figured I'd share what I've been doing after browsing some of the posts on here. I stream sometimes but rarely read chat since I'm focused on the keys I'm doing or the people I'm playing with so feel free to ask questions here or add my Btag Sadlo#1909 most mage streamers are also super informative if you ask 1 or 2 specific questions without bombarding them

Again this is just a general what I do/think about when playing fire. if my group doesn't have a slow I play frost if my tank needs it.

General Azerite:

Using the talent setup with Pyroclasm:

I've been messing with Wildfire x 2 or x 3 with Archive filling in the blanks and it comes down to procs. I like this playstyle on trynical but overall dmg suffers from it. I can do anywhere from 15k with no procs on a boss to 25k with good procs...

I've also tried Wildfire x 1 and Archive x2, similar to 2/3 it comes down to procs, this setup seems less good for ST and better for aoe, meaning it's probably better to just run meteor and Archive x 3 if you don't need more boss damage.

I am testing out using the engineering helm with Barrage of Many Bombs and I'm liking the results with this as well. I think that any dungeon where the tank pulls big more often it pulls ahead in viability. It's done up to 6.5% of my dmg with good procs in a dungeon which is MASSIVE. (BoMB + WF + ARCH or BoMB + ARCH x 2 both seemed good, WF being better for ST when you get procs and Arch x 2 better for trash.

Using the talent setup with Meteor:

I generally just run Archive x 3 or BoMB and Arch x 2.

Meteor is harder to play around to get the full effect when tanks need to kite in higher keys, sometimes better to go frost or play with pyroclasm if your comp has really good aoe.

Please don't use Kindling. (not yet).

Flame Patch vs Living Bomb vs Conflag and Flame on Vs Phoenix Flames

Flame Patch is what I default to if I'm not used to the tanks pulls. When I get more used to the tanks pulls I use living bomb in dungeons where there are 10+ mobs pulled that need to die FAST. You line up combustion, potion, ROP, and your trinket with this. Flame Patch sims higher but back to the kiting thing, sometimes movement changes what can pump out more damage in certain situations, this is also comp dependant.

I personally use Flame On on Tryn and Phoenix Flames on Fort. If group needs more aoe I use PF and if a group needs more ST i'll use FO. With Pyroclasm I almost always use FO as it makes the ROP/combust much easier to manage and saves a lot of GCDs.

Gear
Sim yourself, not going into too much detail here. Make sure you have a Dread Gladiator's Badge--I prefer this over Baleful because it lines up with combustion perfectly and you get the full benefit the whole time. I also use the Dread Gladiator's Insignia but any good passive trinket is a good option for the second spot. For stats generally Mastery/Crit are even with playstyle and comp swaying what is needed. SIM YOURSELF in multiple situations. If you're trying to push 10s sim a 2 minute boss fight. If you're pushing 17s sim a 4-5 minute boss fight, etc. watch some streams to get an idea on how long certain bosses are. For example, Galavax (sp?) in Temple is the most important boss to kill and it's a 4-5 minute boss fight on higher tyrannical keys. If you destroy that boss and play well in the other areas, the dungeon is easy.

Rotation(s)
Most rotational things are situational with affix and comp, the general ST rotation is similar to raid with opening with PPOT/Fireball into your combustion rotation after placing your ROP (I use scorch with fireblasts since I'm still used to the blaster master rotation). This image that someone sent me in the Mage discord would be the min/max version of the opener, but not many mages do this perfectly every single time. https://images-ext-1.discordapp.net/ext ... height=502

For aoe, you can use pyros on prio targets or FS with FP and rune, again all depends on what is needed on a given pull.

For Living Bomb, always line up with ROP.

For Meteor, always line up with ROP.

That's all for now, let me know other things you'd like to know--again these are just things I do and general advice, I don't plan on going into specifics with this
Edits:
12/30
Talent changes for Bolst/Fort: I've been running Searing/Shimmer/ROP/Phoenix/Frenetic/Flame Patch/Meteor, FS over LB because of bolster, but you can get away with LB if you have more prio dps

Rotational changes for Bolst/Fort: on AOE pot->ROP->Meteor->Combust/trinket->PF->FB->FS->PF->FB->FS->PF->Scorch or FB if it's up->FS then Prio target dmg if needed or hard cast FS.
ST just use PF as a filler and use FB with procs

Thank you very much for the great information. I have been looking into this kind of guide for a long time after BM lost it's power.
It clears a lot of things on my mind now. I have the engineering googles as well. I just need some wildfire items.

I would like to ask about the FlameStrike and Meteor usage as well as some stat prioirty. They are noob questions but have to ask.

1) Since the FlameStrike has 7 seconds duration, is it worth to keep spamming Flame Strike on and on or just focus on prior target during these 7 seconds and just refresh it again in last second?

2) Also the usage of meteor, Is it a good idea to drop the meteor on aoe situations? If the cd is down and there is AOE fight should I drop it or wait for single target?

3) Should we go %14-15 Haste and rest crit focused? How ideal stat priority should be most generally speaking.

First of all, thank you very much for the information that means a lot. I have not played WoW since vanilla.
I play Fire Mage 100lvl.

I would like to know which stats to pay attention to properly align the character building in the future
on icy-veins recommend:
intellect;
mastery;
Versatility;
Haste;
Critical Strike.
some voice in me tells me that after INT, I take Critical Strike.
lots of ppl use haste after intelect ...
I'm confused, who to trust

I am currently in Dalaran (lvl100). what do you recommend for the fastest lvlup. which quests in which area.

I spammed PVP to level up, if you like questing I would just recommend doing the areas that you enjoy doing, efficiency is kind of boring if it's your first playthrough. There's no hard cap for fire for any stats, crit will make the playstyle feel better if that's what you're going for, but highest ilvl will probably be better until you start getting azerite gear.

I'm a pretty competent raider and typically top the damage meters on dps. I'm finding a new love in M+ so I'm trying to min/max it to death. While my single target or burst combos on trash do great, my damage just seems sad in between on aoe. LB seems so clunky in rotation, and it doesn't seem like FP is doing that much. I'm comfortable with conflag, but everything I read says that shouldn't be the choice and I only seem to be contributing every 2 min on my burst. Any suggestions more specifically on aoe damage on trash would be appreciated.